1. Field of the Invention
This invention relates generally to agricultural implements, such as plows, which trip upon encountering an immovable obstruction and then automatically reset in their operative position after having passed the obstruction.
2. Prior Art Devices
Most cultivatable land has at least some hidden obstructions in the soil in the form of large and usually immovable objects such as rocks, roots, stumps, or the like. These objects can cause severe damage to earth working implements which are used in either preparing the soil for seeding or subsequently for cultivating. It is obviously both impractical and impossible to remove all these obstacles; therefore, some provision must be made to avoid damage to the earth working elements of the implement when such elements strike the hidden obstructions.
Various attempts have been made in the prior art to design an earth working implement which can pivot upwardly and backwardly when striking an obstruction, in order to avoid damage to the implement.
For example, many of the previous implements have included a latch mechanism which releases the ground working tool and permits it to pivot upwardly when it strikes an obstruction. The drawback to such prior art devices lies in the fact that once the latch mechanism has been disengaged, the operator must reset the ground working tool either manually or by backing up the entire implement. Such a device is shown, for example, in U.S. Pat. No. 2,690,111 to Altgelt. Because of the inherent drawbacks in the latch-type release mechanism, other prior art attempts at designing a releasable earthworking implement have focused on a spring biased arrangement to maintain the earthworking implement in the ground under ordinary working conditions. However, a common drawback to these type devices is the inability of the spring arrangement to reset the earthworking implement back into the soil after it passes the obstruction. This problem is fully understandable when the various forces working against the downward pivotal resetting movement of the plow are appreciated. First, the downward biasing force must be great enough to cause the plow to penetrate the soil and assume its prior plowing position. Second, a rearward reaction force, which is due to the plow moving forward behind an agricultural vehicle, must be overcome. If these two forces are not overcome, the earthworking implement will not reset properly.
U.S. Pat. Nos. 407,780 to Kissell, 903,117 to Waterman, 2,679,972 to Sheppard, and 3,321,027 to Johnson et al represent prior art devices having a spring biased toggle link assembly to maintain the plow or other earthworking implements in the ground under normal operating conditions. U.S. Pat. No. 3,765,492 to Irwin illustrates another earthworking implement with a tripping mechanism. Other devices have been manufactured which include an elongated pivotal guide surrounded by a compression spring to maintain the earthworking implement in proper position.
A further shortcoming in many of the prior art tripping or releasing mechanisms is due to such implements having linkages, springs, and pivot points located in the region of the earthworking implement. In this position dirt and field debris readily come in contact with the moving parts to interfere with the proper operation of the mechanism and create undue wear on parts which move relative to one another.
In other prior art devices, it has been found that the mechanical arrangement of the spring and linkages fails to properly maintain the earthworking implement in the ground under certain conditions. For example, when the implement is drawn through a region of hard soil, the backward force exerted on the implement is of sufficient magnitude to overcome the biasing force of the spring. As a result, the implement pivots backwardly out of the ground to render it virtually inoperative. Such devices also generally exhibit the inability to properly reset the earthworking implement, as discussed above.
In order to overcome many of the shortcomings previously discussed, many manufacturers have turned to hydraulic cylinders for the earthworking implement biasing means. Hydraulic cylinders have the ability to absorb large amounts of energy, are easy to adjust for various loads and can reset the earthworking implement after having passed an obstruction. However, hydraulic cylinders are expensive, require maintainance and provide a limited amount of movement of the earthworking tool. Further, hydraulic cylinders have a natural tendency to leak, thereby either losing some of their efficiency or requiring the operator to readjust or refill the cylinders. Hydraulic arrangements also have a fixed amount of reservoir fluid. In the situation where a plurality of plows or other earthworking implements are provided on a common plow beam assembly and two or more of the plows simultaneously engage an obstruction, the reset power of the system is greatly diminished because the reservoir fluid has to exert an adequate amount of force on each of the tripped implements.
A more basic shortcoming in almost all of the prior art devices is the failure to provide a reset mechanism having a simple design and a minimum number of parts. Such complex arrangements are, quite naturally, more expensive, thereby causing a corresponding consumer displeasure.
The present invention overcomes these prior art inadequacies and shortcomings, while providing numerous other advantages. For example, this invention employs a linkage arrangement situated above the plow shares so that debris does not engage the pivot points to interfere with proper operation. Further, a compression spring is strategically located at the elbow of a toggle link assembly to eliminate the necessity of a separate latch mechanism and to provide sufficient power to reset the earthworking implement after having engaged an obstruction.